1. Field of the Invention
The present invention relates to a monitoring and control system, and more specifically to a monitoring and control system for automatically monitoring and controlling monitoring and control targets spread out over a wide area, such as switches placed on distribution lines.
2. Description of Related Background Art
FIG. 14 is a drawing illustrating a case where a conventional monitoring and control system is applied to a power distribution automation system under the service area of a sales office. A center system 100 installed in the sales office exists at the center and a substation 1 to a substation 7 (or there exist more or less substations). 101 exist around the center system 100, a plurality of distribution lines 102 extend from each substation 101, normally closed distribution line section switches 104 are placed on respective distribution lines 102 as appropriate, and normally opened distribution line loop switches 103 that are interconnectable with other distribution lines 102 are placed at appropriate locations.
The sales office, in which the center system 100 is installed, is connected to each substation 101 by a communication line 105. Also, each substation 101 is connected to each of switches 103 and 104 by a communication line 102-1. The center system 100 collects information concerning the switches 103 and 104 and the substations 101 and controls equipment of the substations 101 or the switches 103 and 104 on the basis of the information.
FIG. 15 is a detailed explanatory drawing of an example of a construction of a monitoring and control system of this type shown in FIG. 14. In FIG. 15, reference numeral 1 denotes a center system, each of numerals 2-1 and 2—2 denotes a communication line between the center system 1 and a substation terminal 3-1 or 3-2, each of numerals 3-1 and 3-2 denotes the substation terminal, each of numerals 4-1, 4-2, and 4-3 denotes a communication line that extends from one of the substation terminals 3-1 and 3-2 and exchanges information with a switch terminal unit 5-1, 5-2, or 5-3. Each of reference numerals 5-1, 5-2, and 5-3 represents a switch terminal unit that is provided so as to correspond to one of switches 15-1, 15-2, and 15-3 and performs the monitoring and controlling of the switch. Reference numeral 10 denotes a power receiving line of each substation, numeral 11 denotes a main power distribution transformer, numeral 12 denotes a power distribution bus line of each substation, and numeral 13 denotes a feeder circuit breaker (hereinafter referred to as the “FCB”). Each of reference numerals 14-1, 14-2, and 14-3 denotes a distribution line, each of numerals 15-1 and 15-2 denotes a normally closed distribution line section switch that is placed on the distribution line, numeral 15-3 denotes a normally opened distribution line loop switch that is placed on the distribution line, each of numerals 15-4, 15-5, and 15-6 denotes a normally opened distribution line loop switch that is placed on the distribution line and is interconnectable with another distribution line.
An operation will be described. In FIG. 15, if a distribution line fault occurs to a certain section of the distribution line (to the distribution line 14-2, for instance), a protection relay installed in a substation starts its operation and trips the FCB 13, thereby placing the distribution line in a power failure state. At this point, information showing that the FCB 13 is opened, information showing that the protection relay starts its operation, information showing a fact that the distribution line detected by the switch terminal units 5-1, 5-2, and 5-3 is placed in a power failure state, and information showing how a fault current has passed are sent to the center system 1 through the substation terminal 3-1.
FIG. 16 is a drawing showing the flow of information from the center system 1 to the substation terminal 3-1 and the distribution line section switch by the terminal unit. FIG. 16 also shows the types of the information.
FIG. 17 shows a system construction where information in the center system 1 is backed up using a substitute center system. This system construction is, so to speak, a duplex system in which necessary processing is performed by the center system 1 in ordinary cases, but in the case where the center system is temporarily stopped due to a periodical inspection or the like, the center system 1 is switched to the substitute center system and the necessary processing is performed by the substitute center system.
Also, in this drawing, two channels (channel A and channel B) are used as the communication line between the sales office and the substation, so that the reliability is considerably enhanced. However, there are many cases where both of the communication lines A and B fall into a communication failure state at the same time. Representative examples of a factor that causes the breakdown of a communication line are a case where an underground communication line is cut during a road construction work or the like, a case where a communication line is cut by a working vehicle during a construction work in the vicinity of the communication line, and the like. As can be seen from this, there exist various factors causing such a breakdown, and surprisingly, there are many cases where both of the two channels are break down at the same time.
In FIG. 15, the center system 1 analyzes where a fault section is on the basis of the information sent and specifies the fault section. That is, the center system 1 comprehensively puts together the facts that: a fault current has passed through the switch terminal unit 5-1 and the switch terminal unit 5-1 is placed in a power failure state; no fault current has passed through the switch terminal unit 5-2 but this switch terminal unit 5-2 is also placed in a power failure state; the switch terminal unit 5-3 detects that a power failure has occurred at one end thereof and the other end thereof is in a voltage sound state; the substation FCB 13 is opened on the basis of these information; and a protection relay for the distribution line starts its operation. As a result, the center system 1 judges that a section 14-2 is the fault section.
When a fault section is specified, the center system 1 checks whether there exists any sound (fault-free) power failure section of the distribution line. In this case, the section 14-3 is such a power failure section. If there exists any sound power failure section, a switch adjacent to the fault section is turned on and locked, the FCB 13 is turned on to transmit power to a side closer to a power source than the fault section, and it is checked whether a distribution line interconnection switch exists on a side closer to a load than the fault section. If the judgment result is positive, the interconnection switch is turned on to transmit power to the load-side sound power failure section in the fault section.
The conventional system is constructed and operated in the manner described above. Therefore, there occurs a problem that it becomes impossible to perform automatic monitoring and control in the case where a communication line that realizes communication between a sales office and a substation is broken down or in the case where the center system is downed.